The present invention concerns a transmission, especially for twin-screw extruders, with a driveshaft, at least one reduction stage, an output-bifurcating stage, and two output shafts. The reduction stage or stages adapt the speed and torque to various applications.
A transmission for twin-screw extruders of this genus is known from European Patent A 0 670 495. It includes a driveshaft and at least one output shaft. The output shaft is driven by the driveshaft by way of at least one helical driving gearwheel mounted thereon and by way of at least one helical output gearwheel mounted on the output shaft. The gearwheels engage axially movable and helical intermediate gearwheels. The intermediate gearwheels are associated with an axial-force compensator. This transmission distributes the load adequately between the two intermediate gearwheels but is complicated and takes up considerable space.
The object of the present invention is accordingly a completely advanced transmission of the aforesaid genus that will occupy less space and reliably transmit even powerful torques at a speed appropriate for the particular application.
The advantage of the present invention is that, since the sliding bearings occupy less space, the axes of the individual shafts can be closer together even though an equivalent torque is transmitted. It will, however, also be possible to transmit more powerful torques without varying the distance between the shafts by using longer-diameter shafts or gearwheels or, if the shafts lack sliding bearings, larger radial bearings.
The output shafts in one preferred embodiment of the present invention, rotate in the same sense. This embodiment can be employed to drive a twin-screw extruder with screws that rotate in the same sense.
The two output shafts can be even closer together if at least one intermediate shaft is interposed downstream of the output-bifurcating stage and can accommodate at least some of the transmitted output. Such an arrangement will also allow the rotation to be reversed.
The advantage of closer-together output shafts can also be attained if the intermediate shaft merges directly into one of the output shafts.
It will also be possible for the intermediate shaft and one of the output shafts to engage each other directly by way of gearwheels. This arrangement will allow further transmission of output in the opposite sense.
In one practical embodiment of the present invention, opposingly cogged helical gearwheels are mounted the other on the intermediate shaft and one on the output shaft, creating a herringbone gearwheel that eliminates axial force. The result is a distribution of output followed by addition, the output components being precisely equal. This distribution of output allows more gearwheels and bearing to be employed, decreasing the load on the individual components. Another advantage is that the intermediate shaft and the output shaft can be sectioned and connected by a clutch.
The output in one preferred embodiment of a transmission with output shafts that rotate in the same sense is distributed between an intermediate shaft and a output shaft by way of directly mutually engaging gearwheels, the intermediate shaft meshing with another output shaft by way of other gearwheels.
A hydrodynamic film can be created to make them stronger by lubricating the sliding bearings.
This special film on the bearings""surface will allow reliable operation even in a combined-friction range.
Depressions in the bearings""surface can promote formation of the film. To improve introduction of the lubricant and hence promote heat removal, the depressions can be channels. If the channels extend at an angle to the radial plane, the dragging flow of the lubricant can be exploited to remove even more heat, eliminating the usual need for to supply oil under pressure.